Recently there has arisen a growing demand for low cost nonmetallic connectors of simplified design. Because injection molded thermoplastics can be produced cheaply, at least several such connectors have been patented and now appear in the marketplace. One of these is shown in U.S. Pat. No. 3,493,205 to Bromberg, and another is shown in U.S. Pat. No. 3,788,582 to Swanquist. Each of these two designs represent improvements in the state of the art, but each includes certain limitations which have precipitated the present invention. The first of the above described connector patents discloses a connector device or "bushing" comprising a tubular body with tethered clamping means in the form of a "plug". After a cable is threaded through the tubular body, this plug is pressed through a transverse opening in the tubular body into compressive contact against the side of the cable so as to wedge the cable and connector together. In the field, this driving of the plug is normally accomplished with channel-lock pliers or the like.
The other patent mentioned above discloses a two-piece connector comprising a tubular body carrying transversely therethrough a separate but captivated cam element. An enlarged end of the cam element protrudes outside of the tubular body and carries thereon both a hex head and a screw slot of rotating it into compressive contact with a cable extending axially through the connector body. The screwdriver slot extends axially into this enlarged end of the cam element, and thus a limited amount of torque can be applied to the cam element with a screwdriver, this being the usual tool used to attach the cable to the connector in the commercial form of the invention.
Both of these prior art connectors are designed to be pushed into a knockout opening in an electrical box from the outside of that electrical box. When used for "old work" (installation of new electrical lines in an old structure) this presents the dilemma of either ripping away part of the interior wallboard surrounding the electrical box in order to mount the connector into the box from its outside, or alternatively, the connector must be mounted into a knockout opening from the inside of the box, in which case the bulk of the connector is inside the box and limits the available space therein.
In the present invention, the connector is both designed and intended to be mounted into a knockout opening from the inside of the box for both new work and old work. Because the bulk of the connector when mounted is outside the electrical box, except for a thin but solid flange at its interior end, it will both withstand a considerable pullout force as well as consume a minimum of the interior box volume. This connector carries a cam element with a slot therein arranged to receive a screwdriver or the like transverse of its axis to exert a considerable mechanical advantage on the cam resulting in a significant wedging effect on the cable with a minimum of effort on the part of the installer. The uncertainty of prior art connectors as to when the clamping means are completely or securely "driven home" against the cable is eliminated because the cam element of this invention makes an audible "click" after it has been rotated approximately 90.degree. from its open position to its locked position, this 90.degree. rotation being the same for a wide range of cables. To facilitate installation, the tubular body interferes slightly with the rotation of the cam element away from its "open" position so that it is held in that position from the time it leaves its place of manufacture until it is rotated into its "locked" position against the cable by its ultimate user. In order to achieve uniform clamping of cables of different thicknesses, a deformable pressure pad is provided opposite the cam element. The thicker the cable, the more the pad deforms.